Review ArticleMedial Unicompartmental Arthroplasty of the KneeJennings, Jason M. MD, DPT; Kleeman-Forsthuber, Lindsay T. MD; Bolognesi, Michael P. MDAuthor Information From Colorado Joint Replacement (Dr. Jennings), Denver, CO, and the Department of Orthopaedic Surgery (Dr. Kleeman-Forsthuber and Dr. Bolognesi), Duke University Medical Center, Durham, NC. Dr. Jennings or an immediate family member is a member of a speakers' bureau or has made paid presentations on behalf of Xenex; serves as a paid consultant to Total Joint Orthopedics; and has received research or institutional support from DePuy Synthes. Dr. Kleeman-Forsthuber or an immediate family member is an employee of Arthrex. Dr. Bolognesi or an immediate family member has received royalties from Total Joint Orthopedics and Zimmer Biomet; is a member of a speakers' bureau or has made paid presentations on behalf of Zimmer Biomet; serves as a paid consultant to Total Joint Orthopedics; serves as an unpaid consultant to Amedica and Total Joint Orthopedics; has received research or institutional support from Zimmer Biomet and DePuy Synthes; has received nonincome support (such as equipment or services), commercially derived honoraria, or other non–research-related funding (such as paid travel) from AOA Omega; and serves as a board member, owner, officer, or committee member of the American Association of Hip and Knee Surgeons and the Eastern Orthopaedic Association. Journal of the American Academy of Orthopaedic Surgeons: March 1, 2019 - Volume 27 - Issue 5 - p 166-176 doi: 10.5435/JAAOS-D-17-00690 Metrics Abstract Indications for medial unicompartmental knee arthroplasty (UKA) have expanded over the past two decades. Proposed advantages include faster recovery, improved kinematics, and better functional outcomes compared with total knee arthroplasty (TKA) in age-matched control subjects. A focused preoperative examination and imaging is essential to identify appropriate surgical candidates. No difference has been demonstrated between fixed- and mobile-bearing implants for implant survivorship or patient-reported outcomes. The most common reasons for conversion to a TKA are aseptic loosening and progression of osteoarthritis. Ten-year survival for UKA in cohort studies has shown to be >90% with outcomes after conversion to TKA being similar to outcomes for revision TKA. Registries have consistently shown lower implant survival for UKA compared with that for TKA, which is likely secondary to use of several different implants by surgeons of varying levels of experience. UKA has the potential to be a cost-effective alternative to TKA in certain patient populations when performed at high-volume centers with advanced surgical techniques. Copyright 2018 by the American Academy of Orthopaedic Surgeons.